Method of uniting layers of rubber of unlike character



G. E. LANGFORD.

METHOD 0F uNmNG LAYERS 0F RUBBER of uNLlKE CHARACTER.

APPLICATION FILED SEPT. I5, I92I. K

Patented Jan. 10, 1922'.

@u /WJ @MM/@MMM GEORGE E. LANGFORD, 0F WASHINGTON, DISTRICT 0F COLUMBM.

METHOD 0F UNITING- LAYERS 0F RUBBER OF UNLIKE 1 "i ,'1

Maaate., l

Specification of Letters Patent.

Application led September 151, 1921. Serial No. 500,728.

To all whom t may concern a Be it 'known that l, Geenen E. LANGroRD, a citizen of the United States of America, 'and resident of Vashington, in the District of Columbia, have invented cert-ain new and useful Improvements in Method ot Uniting Layers of Rubber ot' Unlike Character', ot' which the following is a specification.

This invention relates toa process for treating vulcanizable rubber, and has for an object to provide for the production of nished rubber, the layers of which ma)v be ot different degrees o t hardness wherein the joint bet-Ween the layers of rubber is properly cured to effect a union of the hard and soft rubber without any weak joint between the said layers. Furthermore, lthe material at the joint between the layers of rubber is strong and durable, and will not: deteriorate while in use to a greater extent than the layers of rubber which it unites.

lit iswell known that heretofore where layers of rubber are to be vulcanized together and where one layer is composed ot' rubber and sulphur, which sulphur may be termed the vulcanizing agent, in such proportions as to produce a/hard rubber and the first mentioned layer is to be joined to a layerl composed of rubber and sulphur proportioned to produce sott rubber, diiiculty has been experienced in uniting these layers of rubber of unlike characteristics, as the 'oint or the material vinterposed between the layers to form the bindingl agent is usually undercured or overcured as compared -with Ythe layers which it unites, and the agent employed as the binder deteriorates more rapidly than'the rubbers which it unites.

The inventor has, by a: novel method, e'ected a union or joint between rubbers ot unlikei characteristics which overcomes the objections noted, producing a superior product, and when this method is employed in the manufacture of solid or cushion automobile tires or rubber heels for shoes, and other rubber articles, he has been ablef to yunite a hard, strong and tough base with a yielding,'cushioning tread surface in such a manner that there is no liability of the breaking down of the joint between the two. lin fact, he has found that where strain is exerted on the materials, a break will occur at places awa from the jointrather than at the jolnt, an so the superior'quality of the union will be apparent.

llt 1e a further object of this invention toiy vulcanize the layers of rubber when the proportlons of rubber and sulphur vary in the compositions, using a vulcanizable gum between the layers ot rubber which are impregnated with sulphur, the said binding agent being preferably' free of sulphur,

lalthough results are attainable with the use of a small percentage of sulphur in the binder. By the term binder the inventor refers to the material employed to control the migration of sulphur and the material which may be said to form the joint.

In describing the invention in detail, ret, Eerence will be had to the accompanying drawings forming part of this application 1n which a shoe heel is illustrated composed Patented Jamil@ 1922,'

ot' layers of rubber, the layers having variable vdegrees of sulphur in them, whereas the binder, in the present embodiment, is entirely free of sulphur.

In carrying the invention into practice, li employ rubber and sulphurv together with the desired fillers, accelerators and the like, as known in the art, in such proportions as will give the desired characteristics to the .layers of rubber which it is intended to unite. For a base, it is usually preferable to have a high percentage of'sulphur to give rigidity to the product, and while the inventor does not wish to be limited with respect to the proportions, he yhas found that a composition having twenty-six per cent ot crude rubber, forty-two per cent bf re claimed rubber. and sixteen per cent of sulphur, with fillers and accelerators to makeV one hundred per cent when properly vulcanized will produce a relatively hard,'

strong base, although said base will not be brittle. A greater or smaller percentageot` sulphur can be employed, as one skilled in the art will understand.

Associated with this composition having sixteen per cent of sulphur, l employ a coml position having forty-two per cent of crude rubber and two per cent of sulphur together with lillers to make one hundred per cent, and which when properly vulcanized, will produce a strong and tough, but resilient and cushioning rubber, and when these two compositions above referred to, are vulcanized at the same temperature and for the same length of time, their characteristics will be quite unlike each other. In order to produce the feint or bond between these rubbers of un ike characters having the du` rability of which mention hasbeen made, a

ywithout sulphur will be vulcanized to a degree which will produce the jointdescribed. In some cases, a layer of crude rubber without sulphur, and without fillers can be used to advantage.`

Soft rubber is properly produced when containing from two to three per cent of combined'sulphur while hard rubber contains as high as thirty-two per cent of combined sulphur, and theinventors theorywith respect to the joint or bond described above is that the sulphur in the highly impregnated layer migrates and impregnates the layer of rubber which is without sulphur'to such an extent as to make it vulcanizable. Where a layer of rubber impregnated'with sulphur is employed to form the joint between the rubbers of unlike character, an excess of sulphur develops in the binder due to the migration o-f the sulphur from the more highly impregna-ted layer, and in the processes heretofore employed in which the binder is impregnated with sulphur, the binder becomes vovercured or so otherwise affected to a degree where an imperfect joint results. .i

The thickness of the layer of rubber with-- out sulphur which is'employed between the layers containing sulphur will depend upon the thickness and percentage of sulphur in the more highly impregnated layer and the temperature and time of cure. For layers substantially the thicknesses shown in the drawing, the thickness of the rubber with! out sulphur indicated in the drawing is` ap proXimately the correct proportion, although obviously one skilled in the art may modify the same within certain proportions withoutdeparting from the spirit of the invention.

I claim:

1. The herein described method of uniting masses of rubber of unlike' character, consisting in interposing rubber without sulphur between vulcanizable masses of rubber having sulphur of unlike proportions, and in vulcanizing the said masses.

2. A method of controlling the migration of a vulcanizing agent when producing and joining or uniting hard and soft rubber by vulcanizing, consisting in interposingprubber free of a vulcanizing agent between and in contact with masses of rubber prepared to produce the hard and soft rubber and GEORGE E. LANGFORD. 

